Especially in the field of industrial cutting up of meat, it is necessary that the butchers at all times have access to sharp knives. A knife edge is ground such that the edge angle provides a correct cutting edge. The curvature of the edge line is corrected, and the edge line will lie in a plane which usually is the symmetry plane of the knife. Such a finishing operation can be performed in several steps, that is first a coarse grinding and then a fine grinding. Before and during the meat cutting work, the butcher must further finish the knife edge by means of a so called finishing steel, that is a substantially smooth steel rod, which generally is moved along the knife edge in order to provide the edge with a curvature as sharp and smooth as possible.
This "steeling" is important, especially in connection with cutting away meat from bone, as a steeled knife edge is a prerequisite in order to avoid damages to the knife edge or avoiding the knife edge cutting into bone when the knife is moved adjacent the bone. The steeling operation develops a knife edge that becomes smooth and straight so that the knife edge, in microscale, does not develop a saw tooth configuration in the plane of the knife blade or any wave shape along its length across said plane of the knife blade.
Correct use of a steel (sharpening steel) requires substantial practice, and many butchers cannot learn the technique, because the correct use is that the sharpening steel is held with a correct angle to the knife edge plane and an erroneous angle means that the steeling operation will produce a blunter knife or means that the edge is not effected by the steeling. The sharpness of the knife is decisive for the working capacity of the butcher and the cutting up yield, because a blunter knife requires exertion of more power and, therefore, reasonably reduces the working capacity of the butcher, and also causes a risk of a lower yield of meat from the cutting up operation.
An apparatus for the sharpening of a knife is previously known and comprises a stand with a holder for the knife, a whetstone and a rod which is fixedly connected to the whetstone and pivotably mounted in the stand so that the whetstone is arranged with a predetermined, substantially constant angle to the plane of the knife blade. By displacing the whetstone along the knife edge, it is possible to finish one side of the knife edge in the desired manner and thereafter the knife is detached from the holder and turned for finishing of the other edge side. However, there is no possibility of periodically shifting the edge treatment position of the whetstone from one edge side to the other during a knife sharpening operation, and therefore the known apparatus does not offer any useful sharpening of the knife since after treatment of the knife in the known apparatus, the knife must be further treated for removal of burr formed on the knife edge, and the knife edge must be steeled in order to be brought to required sharpness for effective use.
An object of the invention is to provide a knife sharpening process and an apparatus which offers fully acceptable sharpening including steeling of a knife without reliance on the operator's ability intuitively to feel whether or not the treatment leads to the decided sharpness for the knife edge.